1. Technical Field
The present invention relates to a synchronous control apparatus, and particularly to a synchronous control apparatus that synchronously operates a main shaft and a driven shaft with an arbitrary gear ratio.
2. Related Art
A programmable logic controller (hereinafter, referred to as a “PLC”) is made up of a plurality of units including, for example, an arithmetic operation unit that executes a user program, an IO (Input Output) unit responsible for signal input from an external switch or an external sensor, and signal output to an external relay or an external actuator, and the like. The PLC executes control operation while giving and receiving data via a PLC system bus and/or a field network in every user program execution cycle among the above-described units.
As control of operation of machinery, equipment and the like, motion control to control a motion of a motor may be included. As a representative example of the above-described motion control, an application that performs positioning of a mechanical mechanism such as a positioning table or robot is assumed.
In a motion controller, synchronous operation and synchronous control means systems in which a main shaft and a driven shaft are operated while maintaining some relationships, and generally include cam operation and gear operation. The cam operation is a system of searching a position (displacement) of the driven shaft corresponding to a position (phase) of the main shaft from a cam table in each control period to decide a command position of the driven shaft. The gear operation is a system of determining the command position of the driven shaft with a value obtained by multiplying a velocity of the main shaft by the gear ratio used as a command velocity of the driven shaft.
In a position control system performing the synchronous control, when a cam curve is switched, a position target value (position command value) becomes discontinuous, causing vibration and impact.
Against this problem, for example, in Japanese Unexamined Patent Publication Nos. S59-183413 and H5-127731, there is disclosed a technique of generating an orbit (a curve of a command value) so that a position and a velocity are not discontinuous at an end of a connection section of the cam curve.
However, in Japanese Unexamined Patent Publication Nos. S59-183413 and H5-127731, a velocity curve needs to be generated in advance, and thus, a user cannot switch the cam curve at arbitrary timing.
Moreover, in Japanese Unexamined Patent Publication Nos. S59-183413 and H5-127731, since a higher-order curve in which a derivative value is continuous needs to be generated, complicated software processing is required. Thus, there is a problem that real-time calculation within a control period is disabled in a CPU of a low specification.